Attachments for a ladder which provide an extendable leg are known. For example, U.S. Pat. Nos. 1,177,069 (Verow), 2,555,036 (Husted), 2,783,928 (Cox), 2,911,134 (Derby), 2,914,135 (Crouch), and 4,627,515 (Studer) show various arrangements which provide an extensible leg for holding a ladder level on an uneven surface. Some of these are removably attached to the ladder while others are permanent parts of the ladder structure.
It is also known to provide a ladder with a bubble level to indicate when the ladder is in a desired orientation. For example, U.S. Pat. Nos. 2,845,719 (Thomiszer) and 4,554,994 (Weiner) show bubble levels for indicating when a ladder is leaning at a proper angle against a wall.